The invention relates generally to a cassette for photosensitive material.
More particularly, the invention relates to a cassette for X-ray film.
A known cassette for X-ray film has a bottom portion and a cover which are movable between an open position and a closed position. In the closed position, the bottom portion and the cover cooperate to define a closed compartment for a sheet of X-ray film. Locking elements are provided to arrest the bottom portion and the cover in the closed position. The cassette includes a pair of magnetic sheets as well as an intensifying screen which is located between the magnetic sheets in the closed position of the cassette. The intensifying screen is designed to be located adjacent a sheet of film which is accommodated in the cassette. The magnetic sheets generate a magnetic force of sufficient magnitude to press the intensifying screen into firm engagement with the film. At least one of the magnetic sheets is flexible and such sheet has a size which is at least approximately the same as that of the film. The magnetic sheet which cooperates with the flexible sheet is generally in the form of a steel foil.
It has been found that the conventional flexible magnetic sheets tend to develop ridges when subjected to temperature changes. This is due to the fact that the coefficient of thermal expansion of a flexible magnetic sheet differs from that of the carrier material which serves as a support or matrix for the fluorescent material of the intensifying screen. The tendency of the flexible magnetic sheet to develop ridges presents a problem since it affects the ability of the magnetic sheet to exert a uniform force over the entire area of the film.